EVALUATION OF AUTONOMIC NERVOUS SYSTEM IN PATIENTS WITH HYPERTHYROIDISM

• Main Authors: Jin-Long Chen, 陳錦龍
• Other Authors: Woei-Chyn Chu
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/66685676107251012995

博士 === 國立陽明大學 === 醫學工程研究所 === 97 === Background: The observation that hyperthyroid patients manifest symptoms and signs similar to those of hyperadrenergic states suggests autonomic dysfunctions in hyperthyroidism. Despite many previous studies on the association between hyperthyroidism and the hyperadrenergic state, controversies still exist. The analysis of heart rate variability (HRV) is a useful tool to assess the modulation of cardiac autonomic nervous system and the characteristics of the heart rate dynamics. Among studies using linear analysis of HRV to investigate the autonomic nervous system functions in hyperthyroidism, some disclosed reduced vagal activity, whereas others showed no vagal activity impairment. However, studies on the physiology of the cardiovascular system suggested that the generation of the heart rate signal is governed by nonlinear chaotic dynamics. No study has investigated the nonlinear dynamics of heart rate in hyperthyroidism. Objective: This study was designed to evaluate the impact of hyperthyroidism on the autonomic nervous system via linear and nonlinear analysis of heart rate dynamics in patients with hyperthyroidism. Methods: Thirty-six hyperthyroid Graves’ disease patients (32 females and 4 males; age 30 ± 1 years, means ± SE) and 36 sex-, age-, and body mass index-matched normal control subjects were recruited to receive electrocardiogram (ECG) recording. Time and frequency domain HRV parameters, as well as correlation dimension (CD) and detrended fluctuation analysis (DFA) parameters were computed from the normal R-R interval series. Results: The hyperthyroid patients revealed significant differences (P < 0.001) compared with the normal controls in the following HRV parameters: a decrease in the mean R-R intervals, the standard deviation of R-R intervals (SDNN), total power (TP), very low frequency power (VLF), low frequency power (LF), high frequency power (HF), HF in normalized units (HF%), and CD; and an increase in LF in normalized units (LF%), the ratio of LF to HF (LF/HF), short-term scaling exponent α1, long-term scaling exponent α2, and overall scaling exponent α. Conclusions: Using linear and nonlinear analysis of HRV, we have shown that hyperthyroidism is characterized by concurrent sympathetic activation and vagal withdrawal. This sympathovagal imbalance state in hyperthyroidism helps to explain the higher prevalence of atrial fibrillation and exercise intolerance among hyperthyroid patients. In addition, the decreased CD in hyperthyroid patients implies reduced complexity and impaired tolerance to cardiovascular stresses in hyperthyroidism. Furthermore, some HRV parameters could reflect the disease severity in hyperthyroid patients.